ci: replace Deno workflow with Node.js CI (install + build)

Author: 许君山

.github/workflows/deno.yml

@@ -0,0 +1,39 @@
+name: Node.js CI
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+permissions:
+  contents: read
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "20"
+          cache: "npm"
+          cache-dependency-path: |
+            backend/package-lock.json
+            frontend/package-lock.json
+
+      - name: Install backend deps
+        working-directory: backend
+        run: npm ci
+
+      - name: Install frontend deps
+        working-directory: frontend
+        run: npm ci
+
+      - name: Build frontend
+        working-directory: frontend
+        run: npm run build